This invention relates generally to the field of carburetors for internal combustion engines. More specifically, this invention relates to a dual barrel side draft carburetor for motorcycles.
Motorcycles engines, like most internal combustion engines, require a proper mixture of fuel and air to be fed into the combustion chamber of the cylinders. A common device for regulating the air/fuel mixture and delivering it to the combustion chamber is a carburetor. The carburetor controls engine fuel and air input and therefore greatly influences power output. The carburetor mixes fuel and air in the correct proportions for engine operation and atomizes and vaporizes the fuel/air mixture to facilitate combustion. While fuel injection has replaced carburetors in many of today""s vehicles, carburetors continue to be used in high performance vehicles (i.e., race cars) and in motorcycles, particularly where space, cost, or performance preferences dictate.
Carburetors often have the same basic structure: a fuel inlet and reservoir (the fuel bowl assembly), which takes in and holds fuel for metering in the proper proportions; a main body, including a throttle valve and air passage, which admits air in one end and discharges the fuel/air mixture from the other; and one or more fluid circuits connecting the fuel bowl assembly to the main body. The actual design and orientation of the structures varies widely depending on the size, configuration, and performance needs of the engine.
Motorcycles may employ a side draft carburetor. Various examples of side draft carburetors for use in motorcycles are shown in U.S. Pat. No. 5,480,592, issued to Morrow; U.S. Pat. No. 5,128,071, issued to Smith et al.; and U.S. Pat. No. 4,913,855, issued to Panzica, all of which are incorporated herein by reference.
But motorcycle engines may include one or more cylinders. Carburetors on motorcycles, including the carburetors disclosed in the aforementioned U.S. Patents, have conventionally been of the single barrel type. These single barrel carburetors must be designed to supply the appropriate amount of air and fuel to each cylinder of the motorcycle. This is often a difficult task. The manifolds for the different cylinders are usually of different lengths. A single barrel carburetor must be configured taking into account the compromise between feeding cylinders operating under different air/fuel delivery conditions. One solution proposed by U.S. Pat. No. 4,204,585 to Tsuboi et al., incorporated herein by reference, proposes using a carburetor for each cylinder of the motorcycle in the case of a multi-cylinder engine. But this increases the complexity of the bike, as well as requires accommodation in the engine envelope, which may already be cramped. In sum, carburetors for high performance motorcycles present specific design considerations not yet adequately met by prior art designs.
These and other drawbacks of prior art carburetors for motorcycles are overcome by the dual barrel carburetor of the preferred embodiments.
It is an object of the preferred embodiments to provide a duel barrel side draft carburetor for use in two cylinder motorcycle engines.
It is further an object of the preferred embodiments to provide a number of external adjustments and interchangeable parts to allow detailed calibration and customization of a carburetor for a particular user""s performance needs. These adjustments and interchangeable parts allow the two cylinders to be tuned independently in a factory calibration.
It is further an object of the preferred embodiments to provide a plenum manifold with a plurality of carburetor/cylinder passages connected by auxiliary passages.
It is further an object of the preferred embodiments to provide an annular discharge booster venturi associated with each barrel of the carburetor.
It is further an object of the preferred embodiments to provide an improved method for manufacturing and calibrating a carburetor through a modular design with interchangeable parts.
It is further an object of the preferred embodiments to provide an improved motorcycle carburetor which provides more horsepower than stock carburetors and all other aftermarket replacement and performance carburetors presently on the market.
It is yet a further object of the preferred embodiments to provide a carburetor having xe2x80x9ctunablexe2x80x9d circuits, i.e., idle circuit, transfer circuit and main circuit, for each barrel of the carburetor implemented by having interchangeable metering restrictions to allow the fuel delivery rate to be factory calibrated.
It is still yet a further object of the preferred carburetor to provide an external fuel bowl sight glass to permit viewing of the float level without disassembling the carburetor; to provide an externally adjustable float level provided by an externally adjustable needle and seat assembly; to provide an externally interchangeable fuel inlet needle and seat assemblies to allow an increase or decrease in the speed of the fuel bowl fill rate; and to provide adjustable idle mixture screws.
A dual barrel carburetor for two cylinder motorcycle engines is an improvement over prior art single barrel carburetors inasmuch as the barrels, by virtue of dedicated fuel metering devices, may be tuned to optimize the performance of the engine. Likewise, a dual barrel carburetor that allows independent calibration is an improvement over prior art single barrel carburetors. Still further yet, a dual barrel carburetor that permits external adjustment of the fuel bowl fill rate, fuel bowl fill level, and idle fuel mixture is an improvement over the prior art. A plenum manifold that has separate passages from each barrel of the carburetor to each cylinder, but also has an opening between the passages to allow one cylinder to xe2x80x9cborrowxe2x80x9d a portion of its neighboring air/fuel mixture, is also an improvement over the prior art. Still further yet, an annular discharge booster venturi providing even fuel distribution is an improvement over the prior art.
The invention of the preferred embodiments is also directed to a method of manufacturing and calibrating dual barrel carburetors. The preferred method includes a modular design and interchangeable parts. This also is an improvement over the prior art.
The inventive carburetor may be either original equipment sold with the motorcycle or an after-market performance add-on to replace an existing carburetor on a motorcycle. In any event, dynamometer testing has unexpectedly revealed that the carburetor of the preferred embodiments delivers more horsepower than prior art stock carburetors, including original equipment and after-market add-ons.
These and other objects of the preferred embodiments are particularly achieved by a dual barrel carburetor assembly for a motorcycle. The carburetor has a main body forming a first body passage and a second body passage. Each body passage has an intake port, a discharge port, and a main venturi or constriction. A first butterfly throttle valve is disposed within the first body passage between the constriction and the discharge port. The first butterfly valve can be operated to regulate airflow through the first body passage. Similarly, a second butterfly throttle valve is disposed within the second body passage. It is also located between the constriction and the discharge port and can be operated to regulate airflow through the second body passage.
A fuel bowl assembly comprising a fuel intake valve and a fuel bowl body is also included. The fuel bowl body forms a reservoir for fuel. At least one fluid channel connects the reservoir in the fuel bowl to the first body passage and the second body passage. Fuel enters the carburetor assembly through the fuel intake valve and accumulates in the reservoir. Fuel is aspirated as it is combined with air entering the intake end of the first body passage and air entering the intake end of the second body passage. Finally, the air/fuel mixture exits the discharge ends of both body passages.
A plenum manifold may be attached to the main carburetor body to connect the main body to the engine cylinders. The manifold preferably has a first manifold passage and a second manifold passage. The manifold passages have respective discharge ports to the engine cylinders, as well as a main body associated with respective barrels in the main carburetor body. The manifold passages and the main body passages are aligned to form a substantially contiguous air fuel passageway through the carburetor assembly. The first manifold passage and the second manifold passage communicate with one another to allow the fuel/air mixture in each to pass between the two passages depending upon the operating condition of the bike.
In its most basic form, the invention of a preferred embodiment is directed to a carburetor assembly for a motorcycle comprising a main body forming a first body passage having an intake port, a discharge port, and a constriction; a second body passage having an intake port, a discharge port, and a constriction; a first valve disposed within said first body passage between the constriction and the discharge port of the said first body passage, said first valve operable to regulate airflow through said first body passage; a second valve disposed within said second body passage between the constriction and the discharge port of said second body passage, said second valve operable to regulate airflow through said second body passage; a fuel bowl assembly comprising a fuel intake valve and a fuel bowl body forming a reservoir; at least one fluid channel connecting said reservoir to said first body passage and said second body passage; and whereby when fuel enters said carburetor assembly through said fuel intake valve and accumulates in said reservoir, fuel is aspirated within said at least one fluid channel, and aspirated fuel is combined with air entering the intake end of the first body passage and air entering the intake end of the second body passage. Finally, the air fuel mixture exits the discharge end of the first body passage and the discharge end of the second body passage.
Other objects, features and advantages of the preferred embodiments will become apparent to those skilled in the art when the detailed description of the preferred embodiments is read in conjunction with the drawings appended here.